1. Field of the Invention
This invention relates to non-stressed, reinforced cement-containing pipe and more particularly to non-stressed, reinforced, high strength, cement-containing pipe, especially asbestos-cement pipe characterized by high bursting strength and high flexural strength, and a method for producing such pipe.
2. Description of the Prior Art
U.S. Pat. No. 3,631,897 and 3,813,098 disclose stressed concrete or asbestos-cement pipe and other tubular articles wherein tensioning strands of nylon, polyester or polypropylene are wrapped or wound around the surface of the pipe and tubular article and are stretched to a length at least 5% greater than its stable, relaxed length. The material of the strands is fixed in its stretched or elongated condition around the pipe and tubular article, and the material of the strands fixed around the pipe and tubular article is in tension in an amount of 15% or more of its ultimate breaking strength. U.S. Pat. Nos. 2,251,205; 2,375,971 and 2,711,291 disclose concrete pipe having metal wire, such as steel wire, wound around the pipe to reinforce it. U.S. Pat. No. 2,791,241 relates to fibrous reinforced resin pipe comprising a first series of long reinforcing fibers of glass or asbestos helically wound at a helix angle of from 2.degree. to 10.degree., and a second series of the aforementioned long reinforcing fibers superposed on the first series of helical winding and helically wound with a helix angle of from 80.degree. to 88.degree.. A cured resin secures the fibers together to form an integral pipe.
An important application of asbestos-cement pipe of the prior art consisting of asbestos fiber, cement and silica has been for conveying or conducting water under pressure. Cast iron pipe is also utilized in the prior art for conducting water under pressure. The cast iron pipe may require the installation of a sacrificial or impressed current cathodic protection system, not required by asbestos-cement pipe, to obviate corrosion of the iron pipe. The cathodic protection requirement adds materially to the cost of the cast iron pipe. Further, there is room for improvement of the bursting strength, as well as the flexural strength, of the aforementioned prior art asbestos-cement pipe.